This invention relates to heterogeneous metal catalysts. In particular, this invention relates to the catalysts, methods of preparing them, and their use in the production of unsaturated hydroxyalkyl esters.
The catalyst art has long recognized the utility of certain phosphate and metal phosphate catalyst compositions. Among such materials are aluminum phosphates, both stoichiometric AlPO.sub.4 and non-stoichiometric Al(PO.sub.4).sub.x where x is less than 1. For instance, U.S. Pat. No. 3,904,550 describes the preparation of such materials and their use as desulfurization catalysts. U.S. Pat. No. 3,801,704 teaches that aluminum phosphates can be used for catalytic dehydration. U.S. Pat. No. 4,524,225 demonstrates that such phosphates also function as hydrogenation catalysts. Other cited uses of aluminum phosphates include cracking (U.S. Pat. No. 4,382,878), ether rearrangement (U.S. Pat. No. 4,538,008), and polyolefin synthesis (U.S. Pat. Nos. 4,364,839; 4,547,479; 4,424,139; 4,397,765; 4,596,862; 4,504,638; and 4,364,854). In all of these cases stoichiometric or non-stoichiometric aluminum phosphates are taught and methods for making them described.
Among other phosphate-containing catalyst compositions described in the art are strontium compounds described in U.S. Pat. No. 4,505,784 as useful for the synthesis of various amines and other nitrogen-containing compounds.
Iron phosphates, usually both stoichiometric and crystalline, are also well known, but have none of the properties required for catalyst or catalyst support applications. For instance, Tsuhako, et al., (Nippon Kagaku Kaishi, No. 2, 1980, pp. 176-180) describe the preparations and properties of eight crystalline iron phosphates all of which are stoichiometric and have PO.sub.4 /Fe ratios greater than 1.0. Leumann and Lutz, (Galvanotechnik, Vol. 68, No. 8, 1977, pp. 715-719) among others have described the "iron phosphates" which are produced in the treatment of phosphate-containing wastewaters. Such materials are usually stoichiometric FePO.sub.4 and, again, are not catalytic materials.
The art has long recognized the utility of the addition of alkylene oxides to acrylic or methacrylic acid, always in the presence of appropriate inhibitors, to produce 2-hydroxyalkyl (meth)acrylates. A catalyst is always required for this addition. Catalysts mentioned in the art include ammonium salts (U.S. Pat. No. 3,059,024), ammonium ion exchange resins (British Patent 1003346), phosphonium salts (German Patents 2527116 and 2527117), and lithium, sodium and potassium salts of the (meth)acrylate anion (Japanese Patent 7251382; French Patent 1556337; and U.S. Pat. No. 3,214,988). A number of transition metal catalysts, as salts, are also known to the art, including copper (U.S. Pat. No. 3,709,928), titanium (Japanese Patent 6902686), vanadium (Japanese Patent 8187537), niobium or ruthenium (U.S. Pat. No. 4,223,160), chromium (U.S. Pat. No. 4,404,395), and iron (U.S. Pat. No. 4,365,081).
Of these catalysts, the iron salts are the ones most frequently taught in the art as catalyzing the production of 2-hydroxyalkyl (meth)acrylates from alkylene oxides and acrylic or methacrylic acid. The chromium salts are second most frequently taught in the art. British Patent 1003346, French Patents 1357422 and 1357423, U.S. Pat. Nos. 3,804,884 and 3,340,295, Belgian Patent 657517, Netherlands Patent 6700738, and Japanese Patent 7017662, all of which teach the use of ion exchange resins as catalysts, teach the use of heterogeneous (that is, insoluble throughout the reaction) catalysts in the production of 2-hydroxyalkyl (meth)acrylates from alkylene oxides and acrylic or methacrylic acid. Most often, the catalyst is soluble in the reactants and the products, and a separation step of the product from the catalyst is required.
This discussion of the prior art is presented to show the various compositions and methods of preparing such compositions which are well known in the existing art, and to show the types of catalysts that are well known in the existing art to promote the formation of 2-hydroxyalkyl (meth)acrylates. These documents are only illustrative of a large body of patents and articles, but the documents cited are believed to reflect the teachings most relevant to this invention.